Paraffin Immunofluorescence Increases Light-Chain Detection in Extra-Renal Light Chain Amyloidosis and Other Light-Chain-Associated Diseases.

Abstract

Distinguishing the different types of amyloid is clinically important because treatments and outcomes are different. Mass spectrometry is the new gold standard for amyloid typing, but it is costly and not widely available. Therefore, immunolabeling remains the first step in identifying the most common types of amyloidosis. In amyloid subtyping, direct immunofluorescence works well when applied to frozen sections, but immunohistochemistry on formalin-fixed, paraffin-embedded material often yields poor results, particularly for light chain amyloidosis. Recently, paraffin immunofluorescence has been described as a valuable salvage technique in renal pathology when frozen sections are not available but it has not been evaluated for extra-renal diseases. To evaluate the use of paraffin immunofluorescence for light-chain detection in extra-renal amyloidosis and other light-chain-associated diseases. First, we compared the staining intensity of both light chains between paraffin immunofluorescence and immunohistochemistry on a retrospective cohort of 28 cases of amyloidosis that have been previously typed. Then, we studied the role of paraffin immunofluorescence as an addition to our classical immunohistochemistry panel for amyloidosis typing. In the retrospective cohort, we found that paraffin immunofluorescence outperformed immunohistochemistry for light-chain detection. Then, in the prospective part of the study, we showed that the proportion of correctly classified cases increased from 50% to 71.9% with the adjunction of second-intention paraffin immunofluorescence to the immunohistochemistry procedure. We therefore view paraffin immunofluorescence as a significant addition to the routine workflow for detection of light-chain-related diseases.